Methacrylonitrile vehicle for vesicular photography and method of using same



United states Patent 3 1.61 511 PvHETHACRYLONHTRHiE i IEHlCLE FQR VESHCU- gLAAIEHOTOGRAPHY AND METHUD 0F USlNG Rienzi B. Parker, Era, Weston, and Brian V. Mulder, Cambridge, Mass, assignors, by mesne assignments, to Kalvar Corporation, New Orleans, La, a corporation of Louisiana No Drawing. Filed May 3, 1962, Ser. No. 192,067 2 Claims. (Cl. %49) The present invention relates to photography and more particularly to the production of vesicular images in water insensitive photographic materials.

Vesicular images are formed in a photographic film by small bubbles or vesicles of gas which are formed and trapped in the areas of the film exposed'to light and which refract light. Generally speaking the film has a colloid or a resin coating or vehicle on a backing material and a light-sensitive agent or sensitizer, most commonly a diazo compound, dispersed throughout .the coating. When the film is exposed to light, the sensitizer releases molecules of a gas-nitrogen inthe case of diazo compounds. These do not form vesicles immediately, but they do so when the film is heated, presumably because the vehicle is relaxed sufiiciently on heating for the gas molecules to form bubbles and for the bubbles to expand. The resulting vesicles make the vehicle opaque to transmission of light in the exposed areas and also reflect and scatter light so that they appear white.

The early vesicular materials employed gelatin as the vehicle. These suffered from the difiiculty that the vesicular images obtained faded rapidly. Laterwork has revealed that this problem was caused, in art, by the ed this difliculty is described in the copending application of James and Parker, Serial No. 623,050, now US. Patent 3,032,414. In that improvement, a vehicle is prepared from certain non-hygroscopic resin materials which are combined with a sensitizer in an organic solvent for the components. A uniform water-free mixture of the components is formed in the solvent and this can be applied to the backin g to form the vehicle.

Non-hygroscopic resin materials which are described stant for nitrogen within the range of 8.6 10" to 8 l0- to avoid escape of the gas before development and nevertheless permit diffusion of the gas to form vesicles duringthe development. The preparation of the vehicle must also avoid unduly high temperatures and other conditions which lead to the decomposition of the sensitizer.

Another difiiculty with earlier vesicular record materials is sensitivity of the developed image to high temperature. Normally, the image is preserved because the vehicle is rigid and the vesicles are fixed in place. The rigidity of the vehicle is reduced during development to permit gas molecules to diffuse together to form the vesicles and for expansion of the vesicles, but it is thereafter restored by cooling to give permanency to the image. To be truly permanent the vehicle must remain 3,161,511 Patented Dec. 15, 1964 rigid under the conditions to which his exposed, such as heat and moisture.

The present invention is based upon the discovery that a satisfactory vehicle of the above type can be manufactured using polymethacrylonitrile as the resin matrix. This. polymer has a number of advantages. It is soluble in a number of common organic solvents which are not harmful to diazo compounds, the most often used sensitizer; vesicular materials manufactured from polymethacrylonitrile produce remarkably white and highly stable images, particularly resistant to heat.

Another advantage is that polymethacrylonitrile is a homopolymer which is easier to manufacture. Although some homopolymers have hitherto been found satisfactory, many do not have desirable properties. Conse quently, it has been necessary to use copolymers in many cases, and certain copolymers have been found to be highly satisfactory. Nevertheless, homopolymers are preferable because they are easier to manufacture.

This relative ease of manufacture follows from the difiiculty of controlling proportions when there are two or more monomers. Generally speaking, monomers do not polymerize at the same rate; if two monomers are polymerized together, one will enter into the reaction more easily than the other. As the reaction proceeds, this monomer will be consumed more rapidly, and the relative proportions of the two monomers will be changed. Since the rate at which'the monomers enter into the reaction depends on their relative proportions as well as their inherent activity toward the reaction, their reaction rates change. Consequently, as the reaction proceeds, the relative proportion of the monomers entering the growing polymer changes, and the polymer produced at the beginning of the reaction will have difierent monomer proportions from the polymer produced later.

This difliculty can be avoided, in part, by continuously adding monomer during the reaction to maintain constant proportions. However, this is costly and is preferably avoided. It is also possible to accept variations in the proportions of the monomers in the polymer and to thoroughly blend the polymers to assure uniform properties throughout each batch. In many cases, this provides average properties which meet the needs of the product, but this also is; not fully satisfactory. The properties of the product may vary from batch to batch because of variations-in the completeness of the reaction or other conditions. It is preferable to use a homopolymer. 7

The polymethacrylonitrile of the present invention can be prepared by any of the conventional polymerization techniques. For example, it may be polymerized in solution as illustrated by the following Example.

Example I 42.9 g. methacrylonitrile having a boiling point of 87- 89 C. and 0.486 g. benzoyl peroxide were dissolved in 250 ml. of tert-butanol. The solution was gently refluxed at 79 C. for 9' hours. Solvent .was removed and the product was washed with methanol and dried. The yield was 7 /2 grams of polymethacrylonitrile which was soluble in acetone and acetonitrile.

Solution polymerization is advantageous since it is possible to polymerize monomer to completion while dissolved and then to use the solution directly to prepare vesicular films by adding a sensitizer and applying the solution to a backing material.

The sensitizer must be capable of dispersion within the vehicle for the purpose of the required definition as described in the aforesaid James and Parker application.

Among the sensitizers, those which liberate nitrogen units upon irridation such as para-diazo dimethyl aniline zinc chloride are especially valuable although other compounds for example of the type which liberates carbon oxides can be used. The following substances are illustrative of those which are useful:

p-Diazo diphenylamine sulfate, p-diaz-o diethylaniline zinc chloride, p-diazo ethyl hydroxy-ethylaniline zinc chloride, p-diazo'ethyl methyl aniline zinc chloride, pdiazo diethyl methyl aniline zinc chloride, p-diazo ethyl hydroxyethylaniline zinc chloride, 1-diazo-2-oxynaphthalene-4-sulfonate, p-diethylaminobenzenediazonium chloride ZnCl 4-benzoylamino-2-S-diethoxybenzene diazonium chloride, the p-chlorobenzene-sulfonate of 4-diazo-1- cyclohexylaniline, the p-chlorobenzene-sulfonate of 4-diaz-2-methoxy41-cyclo-hexylaminobenzene, the tin chloride double salt of 4-N-methylcyclohexylaminobenzene diazonium chloride, p-acetaminobenzene diazonium chlorid,e 4-dimethylaminobenzene diazonium chloride, 3- methyl-4-diethylaminobenzene diazonium chloride, 4- morpholinobenzene diazonium chloride, 4-piperidyl-2-5- diethoxybenzene diazonium chloride, l-dimethylaminonaphthalene-4-diazonium chloride, 4-phenylaminodiazobenzene diazonium chloride.

The support can be of any suitable material which may be transparent if the exposure takes place therethrough or may be opaque. Of the transparent supports, glass, ethyl cellulose, Mylar (oriented polyethylene terephthalate) and polyolefins and similar substances are satisfactory provided they withstand the operational temperatures required and are relatively free from plasticizers which tend to diffuse into the coating layer of vehicle and sensitizer. Cellulose acetate supports which, generally speaking, are undesirable because they contain diffusable plasticizers, can be used if a suitable barrier layer is interposed between such a support and the layer thereon.

Opaque supports are preferably flexible such as paper or synthetic sheet material. These supports can be of any color, but for certain purposes black supports are particularly suitable. The vesicles or bubbles appear white on such black supports so that a positive image is produced directly. When transparent supports are used, the vesicular photographs can be used as negatives since the light-exposed areas are opaque to transmitted light only.

Any solvent for the methacrylonitrile polymer may be used which is compatible with the sensitizer, as discussed in greater detail in the aforesaid James and Parker application. Acetonitrile is particularly useful. When the solutions are formed, they are coated on a backing in accordance with conventional coating techniques. The solvent is then removed by evaporation and the films are ready for use. After exposure to light in a camera or other suitable device, the films are developed by. heating to an elevated temperature, preferably in the range of 225-300 F. The time of exposure will generally vary inversely with the temperatrure, but will usually be in the range of 1-10 seconds.

The following example illustrate the preparation of a vesicular record material and its use.

Example II 2.1 g. of the polymer produced in Example I was dissolved in 20 ml. acetonitrile by gradual addition to well stirred solvent. The 0.148 g. of diazo compound No. 8 (p-diazodimethylaniline zinc dichloride) were added with agitation. The resulting solution was coated on backings of Mylar (oriented polyethylene terephthalate) and dried for fifteen minutes at 1'1'0l15 C. The films were then exposed to the light from a mercury vapor lamp for various periods of time and developed for three seconds at approximately 250 F.

A clear, white image was obtained which did not fade or become brown after five days at F.

The foregoing description has included specific examples of the invention, but it will be apparent that various modifications can be made without departing from the scope of the invention as set forth in the claims.

What is claimed is:

1. A photographic material capable of furnishing a record solely in the form of a distribution pattern of radiation scattering discontinuities formed within an otherwise substantially homogeneous vehicle, said material being in the form of a dry, Water-resistant non-hygroscopic film, the continuous phase of said film being essentially a synthetic, water-insoluble, non-hygroscopic, nonwater swelling, highly linear thermoplastic homopolymer of methacrylonitrile, and a light decomposable solid agent substantially uniformly dispersed therein as the sole essential decomposable agent, said decomposable agent itself being non-reactive to said vehicle and upon exposure to light decomposing into products which are chemically non-reactive to said vehicle and which solely upon warming are volatile to form said radiation scattering discontinuities only in the light struck areas in said polymer to thereby furnish said record.

2. A method of preparing vesicular images comprising exposing to light a photographic material capable of furnishing a record solely in the form of a distribution pattern of radiation scattering discontinuities formed within an otherwise substantially homogeneous vehicle, said material being in the form of a dry, water-resistant nonhygroscopic film, the continuous phase of said film being essentially a synthetic, water-insoluble, non-hygroscopic, non-water swelling, highly linear thermoplastic homopolymer of methacrylonitrile, and a light decomposable solid agent substantially uniformly dispersed therein as the sole essential decomposable agent, said decomposable agent itself being non-reactive to said vehicle and upon exposure to light decomposing into products which are chemically non-reactive to said vehicle and which solely upon warming are volatile to form said radiation scattering discontinuities only in the light struck areas in said polymer to thereby furnish said record, and thereafter heating said photographic material to develop a vesicular image.

References Cited in the file of this patent UNITED STATES PATENTS 2,787,809 Stasny Apr. 9, 1957 2,996,381 Oster et al. Aug. 15, 1961 3,010,157 Cizek Nov. 28, 1961 3,011,217 Carlson Dec. 5, 1961 3,032,414 James et al. May 1, 1962 3,037,862 Neth June 5, 1962 OTHER REFERENCES Lindquist et al.: IBM Technical Disclosure Bulletin, vol. 4, No.2, July 1961, page 61. 

2. A METHOD OF PREPARING VESICULAR IMAGES COMPRISING EXPOSING TO LIGHT A PHOTOGRAPHIC MATERIAL CAPABLE OF FURNISHING A RECORD SOLELY IN THE FORM OF A DISTRIBUTION PATTERN OF RADIATION SCATTERING DISCONTINUITIES FORMED WITHIN AN OTHERWISE SUBSTANTIALLY HONOGENEOUS VEHICLE, SAID MATERIAL BEING IN THE FORM OF A DRY, WATER-RESISTANT NONHYGROSCOPIC FILM, THE CONTINUOUS PHASE OF SAID FILM BEING ESSENTIALLY A SYNTHETIC, ATER-INSOLUBLE, NON-HYGROSCOPIC, NON-WATER SWELLING, HIGHLY LINEAR THERMOPLASTIC HOMOPOLYMER OF METHACRYLNITRILE, AND A LIGHT DECOMPOSABLE SOLID AGENT SUBSTANTIALLY UNIFORMLY DISPERSED THEREIN AS THE SOLE ESSENTIAL DECOMPOSABLE AGENT, SAID DECOMPOSABLE AGENT ITSELF BEING NON-REACTIVE TO SAID VEHICLE AND UPON EXPOSURE TO LIGHT DECOMPOSING INTO PRODUCTS WHICH ARE CHEMICALLY NON-REACTIVE TO SAID VEHICLE ADN WHICH SOLELY UPON WARMING ARE VOLATILETO FORM SAID RADIATIN SCATTERING DISCONTINUITIES ONLY IN THE LIGH T STRUCK AREAS IN SAID POLYMER TO THEREBY FURNISH SAID RECORD, AND THEREAFTER HEATING SAID PHOTOGRAPHIC MATERIAL TO DEVELOP A VESICULAR IMAGE. 